A glow lamp typically is comprised of a light transmitting envelope containing a noble gas and mercury with a phosphor coating on an inner surface of the envelope which is adapted to emit visible light upon absorption of ultraviolet radiation that occurs when the lamp is excited. The lamp is excited by means of the application of a voltage between the lamp electrodes. Current flows between the electrodes after a certain potential is applied to the electrodes, commonly referred to as the breakdown voltage. An elementary explanation of the phenomenon is that the gas between the electrodes becomes ionized at a certain voltage, conducts current, and emits ultraviolet radiation. Examples of a typical glow discharge lamps are found in U.S. Pat. No. 2,067,129 to Marden; U.S. Pat. No. 3,814,971 to Bhattacharya; and U.S. Pat. No. 4,408,141 to Byszewski, et al.
A standard glow lamp construction as comprised of an envelope that is provided with a phosphor coating on the inner wall of the envelope. The envelope is typically of spherical shape having a generally maximum cross-section bulbous region and also a neck region. There are one or more electron emitting electrodes (cathodes) and one or more electron collecting electrodes (anodes). Typically, a single anode and single cathode are supported in the bulbous region of the envelope. These electrodes may be supported primarily in a side-by-side position.
In the operation of the standard glow lamp, the cathode emits electrons that are accelerated so that mercury vapor is excited in the extended region of the low pressure gas. In this connection the envelope may be filled with a conventional fill material including mercury in a noble gas or a mixture of noble gases. A suitable noble gas is neon or a mixture of neon and argon.
Reference is also now made herein to a co-pending application Ser. No. 07/139,397 now abandoned, filed concurrently herewith on a DC operated negative glow discharge lamp employing a cathode coated with an emissive material and a bare anode. FIG. 1 herein illustrates a glow discharge lamp of this type including an envelope 30 that is provided with a phosphor coating as illustrated at 31. There may be provided one or more electron emitting electrodes (cathodes) and one or more electron collecting electrodes (anodes). FIG. 1, in particular, illustrates a cathode electrode 34 and an anode electrode 36. These electrodes are supported by respective lead-in wires 35 and 37.
In FIG. 1 the envelope 30 is generally of spherical shape having a generally maximum cross-section bulbous region 32 and also including a neck region 33. The lead-in wires 35 and 37 are typically hermetically sealed at the neck region 33 with a wafer stem assembly. In FIG. 1, the electrodes 34 and 36 sup ported primarily in a side-by-side relationship and are approximately at the maximum cross-section bulbous region 32.
In the glow discharge lamp described in co-pending application Ser. No. 07/139,397 now abandoned filed concurrently herewith, the cathode electrode is coated with an emissive material while the anode electrode is uncoated. The anode electrode is typically a bare tungsten coil electrode. The lamp is operated in a DC mode of operation rather than an AC mode of operation.
In the standard glow discharge lamp or the glow discharge lamp of the type described in FIG. 1 herein, we have discovered that an auxiliary electrode may be employed with a getter substance thereon the function of which is to absorb residual gases in the lamp envelope. In this connection refer to, the lamp construction in FIG. 2 in which the same reference characters are employed to identify the same parts previously illustrated in connection with the description of FIG. 1. However, in FIG. 2 it is noted that there is provided an auxiliary electrode 42 positioned in the neck region 33. The auxiliary electrode 42 may be coated with a getter substance such as with a zirconium coating.
There are a number of disadvantages associated with the lamp construction of FIG. 2. The electrode 42 requires separate lead-in wires for support thereof thus making the overall lamp construction more complex. The auxiliary electrode 42 requires a separate electrical heating source to be activated during operation. Thus with the lamp construction of FIG. 2 there is added power consumption and a more complicated overall lamp construction.
A getter technique practiced in the prior art is the use of getter strips, typically sold under the trade name Gemedis. These getter strips are disadvantageous because they need support structures, they require complicated activation procedures, and furthermore require heating during operation for effectiveness. Moreover, placement of a Gemedis strip about the lamp cathode in the glow lamp results in a marked depreciation in light output due to the absorption of exciting radiation by the strip.
The prior art also describes the use of a tantalum anode specifically in vacuum power triodes and tetrodes for use in radio transmitter applications. The anode in such devices operates at incandescent temperatures at which it getters residual gases, preserving the vacuum integrity of the tube.